IMX6 Frame Buffer

ali_sarlak — Wed, 27 May 2015 15:23:03 GMT

Hello

I created a simple program which duty is to draw a vertical line on (frame buffer) ,yet it seems the vertical line doesn’t draw from point (0,0) the actual line is drawn from point (0,3) 3 pixels to the right from origin.

Another problem is, when I use OpenVG to draw something(As you know OpenVG and OpenGL ES use EGL to get native window) in double buffering mode (onscreen to offscreen and vice versa) sometimes I observe flickers on my screen(it quickly moves 3 pixels from left to right and vice versa) and sometimes everything is OK(no any flickers).

I believe the root of above problems lies on Frame Buffer kernel driver in Linux If anyone knows how I can solve the problems please share it with me.

I use L3.0.35_4.1.0_130816_source.

Best Regards:

Ali

Re: IMX6 Frame Buffer

jamesbone — Thu, 28 May 2015 13:53:03 GMT

Hello Ali,

Sometimes the error is in the perspective of the view do you think you can share your code, to review how you are drawing the line?

Re: IMX6 Frame Buffer

ali_sarlak — Thu, 28 May 2015 18:24:00 GMT

Thanks for your reply

The code that I used is from internet, I only changed the main loop on it.

#include <stdlib.h>

#include <unistd.h>

#include <stdio.h>

#include <fcntl.h>

#include <linux/fb.h>

#include <sys/mman.h>

#include <sys/ioctl.h>

int main()

{

int fbfd = 0;

struct fb_var_screeninfo vinfo;

struct fb_fix_screeninfo finfo;

long int screensize = 0;

char *fbp = 0;

int x = 0, y = 0;

long int location = 0;

// Open the file for reading and writing

fbfd = open("/dev/fb0", O_RDWR);

if (fbfd == -1) {

perror("Error: cannot open framebuffer device");

exit(1);

}

printf("The framebuffer device was opened successfully.\n");

// Get fixed screen information

if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {

perror("Error reading fixed information");

exit(2);

}

// Get variable screen information

if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {

perror("Error reading variable information");

exit(3);

}

printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);

// Figure out the size of the screen in bytes

screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

// Map the device to memory

fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,

fbfd, 0);

if ((int)fbp == -1) {

perror("Error: failed to map framebuffer device to memory");

exit(4);

}

printf("The framebuffer device was mapped to memory successfully.\n");

x = 300; y = 100; // Where we are going to put the pixel

// Figure out where in memory to put the pixel

// MAIN LOOP

for (y = 0; y < 800; y++)

for (x = 0; x < 10; x++) {

location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +

(y+vinfo.yoffset) * finfo.line_length;

if (vinfo.bits_per_pixel == 32) {

*(fbp + location) = 100; // Some blue

*(fbp + location + 1) = 15+(x-100)/2; // A little green

*(fbp + location + 2) = 200-(y-100)/5; // A lot of red

*(fbp + location + 3) = 0; // No transparency

} else { //assume 16bpp

int b = 10;

int g = (x-100)/6; // A little green

int r = 31-(y-100)/16; // A lot of red

unsigned short int t = r<<11 | g << 5 | b;

*((unsigned short int*)(fbp + location)) = t;

}

// MAIN LOOP

//Draw 10 W 800 H

munmap(fbp, screensize);

close(fbfd);

return 0;

}

In another board such as BeagleBone Black it draws correctly, but in IMX6 it draws with 3 pixels gap from the left?!

Re: IMX6 Frame Buffer

ali_sarlak — Fri, 19 Jun 2015 19:00:48 GMT

Hello

The problem is with my HDMI to DVI convertor.The cable is cause of the problem.

Best Regards:

Ali

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